The two function seal is required to seal the fluid flow path in gas turbine installations in situations where the jet thrust is required to be vectored such as, for example in vertical take off and landing aircraft. However similar technology may be applied to any installation where there is a fluid flow path, which may need to be vectored.
In the context of this specification the term fluid can refer to gases, vapours or substantially incompressible liquids.
The seals are required to isolate relatively large diameter fluid flow paths —typically covering the range 450 millimeters (18 inches) to 1830 millimeters (72 inches) and, in the case of gas turbine installations, are required to operate over wide and varying temperature ranges from ambient conditions both at sea level and at high altitude conditions rising to, typically, 400 degrees Celsius. The combination of large diameters and wide operating temperature ranges requires a seal which can accommodate significant movements in both the radial and axial directions. In particular, for aircraft vectored thrust jets, the axial movement that has to be covered by the radial faced seal has to be, typically, about one third of the installed width of the seal, for example, on a 1000 millimeter (39 inches) diameter seal the installed width is about 25 millimeters (1 inch) and the axial travel required on the dynamic sealing component is approximately 7 millimeters (0.276 inches). The severe environmental conditions with the relatively large diameters make conventional precision combined face and cylindrical seals unsuitable for this duty.